The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is powered by one or several turbojet engine(s) each housed within a nacelle. The nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a medium section intended to surround a fan of the turbojet engine, a downstream section accommodating the thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally ended by an ejection nozzle located downstream of the turbojet engine.
This nacelle is intended to accommodate a bypass turbojet engine able to generate, by means of the blades of the rotating fan, a hot air flow coming from the combustion chamber of the turbojet engine, and a cold air flow which circulates outside the turbojet engine through an annular channel called flow path.
The thrust reverser device is, during the landing of the aircraft, intended to improve the braking capacity thereof by redirecting forward at least a part of the thrust generated by the turbojet engine.
To do this, the thrust reverser device obstructs at least partially the flow path of the cold air flow and directs the latter forward of the nacelle, thereby generating a counter-thrust which is added to the braking of the wheels of the aircraft.
The means implemented to achieve this reorientation of the cold flow vary according to the type of the thrust reverser. The structure of a thrust reverser generally comprises one or several movable cowl(s) displaceable between, on the one hand, a deployed position in which they open within the nacelle a passage intended for the diverted flow, and on the other hand, a retracted position in which they close this passage. These cowls may fulfill a function of deflection or simply activation of other diverting means.
Moreover, besides its thrust reversal function, the thrust reverser cowl belongs to the rear section of the nacelle and has a downstream part forming the ejection nozzle aiming to channel the ejection of the air flow.
In the case of a nozzle called adaptive or variable nozzle, a section of the ejection nozzle can be adapted depending on different flight phases, namely the take-off, the rising, the cruise, the descent and the landing phases of the aircraft. Advantages of such adaptive nozzles are particularly the noise reduction, the improvement of the motor operability or the decrease of the fuel consumption.
Of course, the nacelles which are not equipped with thrust reverser device, called smooth nacelles, may be independently equipped with a variable nozzle device.
The variation of this section, thus resulting in the variation of the section of the cold air flow path is performed by means of one or more flap(s) of displaceable nozzle.
There are several manners to make the nozzle section vary at the outlet of the nacelle.
According to a first type of nozzle, the variation of the outlet section of the cold air flow path is achieved due to a plurality of flaps, also called deflectors, movably mounted in rotation to a downstream end of the cowl, and adapted to pivot between a retracted position in which they are in the continuity to the aerodynamic line of the secondary air flow path, a deployed position causing a variation of the nozzle section, and a plurality of intermediate positions to said retracted and deployed positions.
This type of adaptive nozzle is particularly suitable for performing a reduction of section relative to its nominal position in continuity to the aerodynamic line of the nacelle.
Systems of adaptive nozzles with pivoting flaps are described in particular in documents FR 2 936 222 and FR 2 934 326.
It will be noted that the nozzle flap can also in some cases serve as blocking flap of the flow path for the thrust reverser device.
According to a second form, the variation of the outlet section of the cold air flow path is achieved by translation of a terminal part of a nozzle cowl.
When the variable nozzle device is associated to a thrust reverser device, the variation of the nozzle section can be performed by partial translation (that is to say shorter than a reversal translation and not activating the diverting means or the cascade vanes) of the cowl of the thrust reverser.
Unlike the previous form, this type of adaptive nozzle is particularly suitable for performing an increase of section relative to its nominal position in continuity to the aerodynamic line of the nacelle.
The nominal position then corresponds generally to the smallest nozzle section.
Some translation systems allow a reduction of the nozzle section, but have in this case only but a small reduction amplitude.
Indeed, in order to obtain a reduction of the nozzle, a translation is performed, not downstream of the nacelle, but upstream of the latter. Given the presence of the medium section and the provision for an overlapping of structures introducing aerodynamic accidents, but also of the cascade vanes housed in the thrust reverser cowl, the amplitude of such movement remains reduced.
Systems of adaptive nozzles with translating cowl are described particularly in documents FR 2 978 802 and FR 2 957 979.